1. Field of the Invention
This invention relates in general to plastic films or membranes containing a medicament, which film or membrane is implanted in tissue or is adhered to tissue, bone, or tooth substrates. The plastic releases the medicament to the substrate over a period of time. In its more particular aspects, the invention concerns an improved polyurethane composition containing fluoride ion and the use of this composition as a dental fissure sealant which also serves as a topical fluoride treatment for the teeth.
2. Description of the Prior Art
In the past, polyurethane formulations based on polyether or polyester prepolymers have been utilized as cavity liners, i.e., resilient formulations interposed between the tooth surfaces and bulk restorative materials applied after removal of carious tissue. For example, U.S. Pat. No. 3,254,411 Shelly teaches such a liner prepared from a tetra-aromatic isocyanate.
An additional later teaching of polyurethanes generally in this art is Galligan et al., The Journal of Dental Research, 47, July-Aug. 1968, p. 629. Previously there has been difficulty with the initial bond strength being fugitive and the physical properties of such liners being degraded in vivo environment.
One approach which has been found to be successful in overcoming such difficulties with prior compositions in this art is to utilize a substantial excess of isocyanate reactant such as from 100 to 1200 percent based upon the available hydroxy groups reacted with the isocyanate group, and based upon the hydroxy reactant derived from a polybutadiene polyol. The handling characteristics of such compositions, however, have not been entirely satisfactory.
Tooth surfaces have been treated topically in the past with a fluoride ion through application of silicate cements containing compounds yielding fluoride ions. Although this process has been somewhat successful, silicate cements are not entirely satisfactory in their handling characteristics nor properties desirable for fissure sealants which require a thin nonporous adherent film resistant to peeling and cracking.